Each state does it in its own way, if at all. Then local cities and provinces do their own thing anyway (sometimes loosening the state-wide rules rather than tightening them).
At least some places the mandates are at the local level and businesses decide for themselves. Example: In-law's business does print advertising. One of their big clients is a fast food chain. So their company lawyers decided they can stay open because they are part of the food business and therefore essential.
No, it's different. Delegated to the states implies that someone else had the power and gave it to the states. That is not true. The states always had the power, and have had it since they formed, and it was not removed upon admission to the United States.
It's like saying France was delegated the power to enforce a national quarantine. That is simply not the case.
It varies a lot by state. I know that here in SF, they had some clear rules (obviously high-contagion things must close; obviously vital things should stay open) with a lot of gray area. But they've been removing the gray area over time. Which I think has been a good approach, as economies are complex.
I am finding confusing information online. Like... Did they really give to the each employer the power to decide if they are essential or not?